1. Field of the Invention
The present invention generally relates to a communication terminal, a communication method, and a communication terminal control program stored in a non-transitory recording medium, each of which is capable of receiving and transmitting location data from or to a transmission system.
2. Description of the Related Art
The location of a user, such as the location of a communication terminal operated by the user, may be determined using a global positioning system (GPS). In the GPS, about 30 GPS satellites that orbit around the earth respectively transmit radio frequency (RF) signals each indicating the signal transmission time. Each of the GPS receivers such as various communication terminals on the earth, receives the signal from the corresponding GPS satellite, and calculates a distance between the communication terminal and the GPS satellite based on the difference between the signal transmission time and the signal reception time. Each communication terminal usually performs this calculation at least for four GPS satellites to determine the location of the communication terminal on the earth.
As the GPS receiver becomes smaller in size and more energy efficient, the use of GPS increases. For example, various communication terminals, such as portable phones, are usually provided with the GPS receivers. However, the communication terminal is not able to receive the RF signal from the GPS satellite, if it is located indoors. In view of this, the indoor messaging system (IMES), which provides indoor positioning, has been proposed to realize seamless positioning environment.